📖 Theory & Concepts ▼

Soft vs Hard Water

Property Soft Water Hard Water
Ions Present Na⁺, K⁺ Ca²⁺, Mg²⁺
Lather with Soap Forms easily Difficult
Scum Formation None White curdy scum
Cleaning Action Excellent Poor

Why Scum Forms

2C₁₇H₃₅COONa + Ca²⁺ → (C₁₇H₃₅COO)₂Ca↓ + 2Na⁺

Soap (sodium stearate) reacts with Ca²⁺/Mg²⁺ ions to form insoluble calcium stearate (scum), wasting soap.

Types of Hardness

  • Temporary: Due to bicarbonates (HCO₃⁻) – removed by boiling
  • Permanent: Due to chlorides/sulphates – needs washing soda
Did you know? Detergents work better in hard water because they don't form scum – they contain synthetic surfactants instead of natural fatty acids!

🎯 Aim

To compare the cleaning action of soap in soft water and hard water by observing lather formation.

🧪 Theory

"Hard water contains Ca²⁺ and Mg²⁺ ions which react with soap to form insoluble scum."
2C₁₇H₃₅COONa + Ca²⁺ → (C₁₇H₃₅COO)₂Ca↓ + 2Na⁺
  • Soft Water: High lather, No scum.
  • Hard Water: Little lather, White scum.

Viva Voce

Q: Why poor lather in hard water?

Select a tube first
0246810
Tube A: Soft Water
0246810
Tube B: Hard Water

Experiment Data

Tube A Lather: 0 cm
Tube B Lather: 0 cm
Observation Log
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